1. Field of the Invention
This invention relates to a rotary oil damper and, more particularly, to an oil damper with oil leakage prevention means.
2. Prior Art Statement
There have been proposed many rotary oil dampers of this type, for instance as disclosed in U.S. Pat. Nos. 4,527,675, 4,614,004, 4,691,589 and 4,691,811.
FIGS. 7 and 8 show a typical two-piece oil damper among the proposed oil dampers. Referring to these Figures, the illustrated oil damper comprises a cylindrical body 1 consisting of a plastic injection molding and open at one end and a rotary member 2 also consisting of a plastic injection molding and rotatably fitted in the cylindrical body 1. An end portion of the rotary member 2 projecting from the cylindrical body 1 has an integral gear 3.
An operating fluid, e.g., viscous grease, is provided in the space between the cylindrical body 1 and the rotary member 2. With the gear 3 meshed with a gear provided on a separate rotary part, resistance against rotation of the separate rotary part is produced by the viscosity of the operating fluid, thus effecting control of rate of rotation of the rotational part.
With this structure, however, the rotary member 2 is merely fitted in the cylindrical body 1. Therefore, the rotary member 2 is liable to be easily withdrawn when it experiences an external force applied in the direction of withdrawing it. Besides, the operating fluid filling the space between the cylindrical body 1 and the rotary member 2 is exposed to the outside from the open end of the cylindrical body 1, which may result in variations of the operating torque over long use. Further, leaking operating fluid is liable to cause contamination.
As measures against these problems, it has been proposed to provide the cylindrical body 1 and rotary member 2 with double-wall cylindrical engagement portions so that it is more difficult for the operating fluid to leak out. Also, there has been developed a structure, in which the edge of the open end of the cylindrical body 1 is formed with a local engagement projection formed with an undercut, and this engagement projection and an engagement projection formed on the outer periphery of the rotary member 2 are engaged with each other to lock the rotary member 2 against detachment.
In the above structures, however, the open end of the cylindrical body remains open so that it is essentially impossible to perfectly prevent the leakage of the operating fluid.